In a small-size blower machine, such as a back-pack-type power sprayer for powder or liquid form chemical by airflow (airstream) discharged from a blower, or a back-pack-type blower for blowing fallen leaves or dust by airstream discharged from a blower, the blower has a fan disposed in a fan case. The fan comprises a base plate, and a plurality of blades arranged on the base in a radial pattern to define a plurality of air passages between the pairs of adjacent blades, respectively. Upon rotation of the fan, air is sucked from a center hub, and discharged to a spiral chamber defined by the fan case through the air passages.
Generally, in operation, the fan generates noise offensive to the operator's ear. Thus, it is desired to minimize such a noise.